Updating and Configuring Published Ports in Docker Swarm Services

You can publish a port for an existing service using the following command: ```console $ docker service update \ --publish-add published=<PUBLISHED-PORT>,target=<CONTAINER-PORT> \ <SERVICE> ``` You can use `docker service inspect` to view the service's published port. For instance: ```console $ docker service inspect --format="{{json .Endpoint.Spec.Ports}}" my-web [{"Protocol":"tcp","TargetPort":80,"PublishedPort":8080}] ``` The output shows the `<CONTAINER-PORT>` (labeled `TargetPort`) from the containers and the `<PUBLISHED-PORT>` (labeled `PublishedPort`) where nodes listen for requests for the service. ### Publish a port for TCP only or UDP only By default, when you publish a port, it is a TCP port. You can specifically publish a UDP port instead of or in addition to a TCP port. When you publish both TCP and UDP ports, if you omit the protocol specifier, the port is published as a TCP port. If you use the longer syntax (recommended), set the `protocol` key to either `tcp` or `udp`. #### TCP only Long syntax: ```console $ docker service create --name dns-cache \ --publish published=53,target=53 \ dns-cache ``` Short syntax: ```console $ docker service create --name dns-cache \ -p 53:53 \ dns-cache ``` #### TCP and UDP Long syntax: ```console $ docker service create --name dns-cache \ --publish published=53,target=53 \ --publish published=53,target=53,protocol=udp \ dns-cache ``` Short syntax: ```console $ docker service create --name dns-cache \ -p 53:53 \ -p 53:53/udp \ dns-cache ``` #### UDP only Long syntax: ```console $ docker service create --name dns-cache \ --publish published=53,target=53,protocol=udp \ dns-cache ``` Short syntax: ```console $ docker service create --name dns-cache \ -p 53:53/udp \ dns-cache ``` ## Bypass the routing mesh By default, swarm services which publish ports do so using the routing mesh. When you connect to a published port on any swarm node (whether it is running a given service or not), you are redirected to a worker which is running that

This section describes how to update an existing service to publish a port using `docker service update` and how to inspect the service's configuration to view published ports. It also details how to specify TCP or UDP protocols for published ports, providing examples for creating services with TCP only, TCP and UDP, or UDP only ports using both long and short syntax. Finally, it introduces the concept of bypassing the routing mesh in Docker Swarm services.